Supercritical boiler for oil recovery

ABSTRACT

Method and systems relate to generating steam by transitioning water from supercritical conditions and injecting the steam that results into a formation to facilitate recovery of oil. Pressurizing and heating the water forms a supercritical fluid that may solvate impurities in the water and/or oxidize the impurities. Retaining the impurities in solution and/or oxidation of the impurities limits fouling problems associated with generating the steam from water recycled in thermal processes, such as steam assisted gravity drainage (SAGD), for recovering the oil.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a non-provisional application which claims benefitunder 35 USC §119(e) to U.S. Provisional Application Ser. No. 61/771,220filed 1 Mar., 2013, entitled “SUPERCRITICAL BOILER FOR OIL RECOVERY,”which is incorporated herein in its entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

None.

FIELD OF THE INVENTION

Embodiments of the invention relate to methods and systems forgenerating steam used in thermal oil recovery processes and that mayfacilitate water treatment and limit fouling.

BACKGROUND OF THE INVENTION

Several techniques utilized to recover hydrocarbons in the form ofbitumen from oil sands rely on generated steam to heat and lowerviscosity of the hydrocarbons when the steam is injected into the oilsands. One common approach for this type of recovery includes steamassisted gravity drainage (SAGD). The hydrocarbons once heated becomemobile enough for production along with the condensed steam, which isthen recovered and recycled.

Costs associated with building a complex, large, sophisticated facilityto process water and generate steam contributes to economic challengesof oil sands production operations. Such a facility represents much ofthe capital costs of these operations. Chemical and energy usage of thefacility also contribute to operating costs.

Past approaches rely on once through steam generators (OTSGs) to producethe steam. However, boiler feed water to these steam generators requiresexpensive de-oiling and treatment to limit boiler fouling problems. Evenwith this treatment, fouling issues persist and are primarily dealt withthrough regular pigging of the boilers. This recurring maintenancefurther increases operating costs and results in a loss of steamproduction capacity, which translates to an equivalent reduction inbitumen extraction.

Therefore, a need exists for methods and systems for generating steamthat enable efficient hydrocarbon recovery from a formation.

BRIEF SUMMARY OF THE DISCLOSURE

In one embodiment, a method of generating steam for oil productionincludes pressurizing and heating water to form a supercritical fluid.At least some of the supercritical fluid transitions to the steam.Injecting the steam into a formation facilitates the oil production.

According to one embodiment, a steam generating system for oilproduction includes a pump having a pressurized fluid outlet throughwhich the pump is configured to provide water at above 22 megapascal toa furnace having a heated fluid outlet through which a supercriticalfluid is provided by the furnace configured to increase temperature ofthe water to above 375° C. A letdown device couples to the heated fluidoutlet of the furnace to receive the supercritical fluid and isconfigured to produce steam from pressure reduction of the supercriticalfluid. An injection well couples with an outlet of the letdown devicefor conveying the steam into a formation to facilitate the oilproduction.

For one embodiment, a method of generating steam for oil productionincludes reducing level of fouling precursors in water by oxidation ofthe fouling precursors in the water at a pressure and temperature abovea critical point thereof. Transitioning the water from a supercriticalfluid forms the steam. Injecting the steam into a formation facilitatesthe oil production.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the present invention and benefitsthereof may be acquired by referring to the follow description taken inconjunction with the accompanying drawings in which:

FIG. 1 is a schematic of a steam generating system for oil productionthat relies on transitioning water from supercritical conditions priorto injection of resulting steam, according to one embodiment of theinvention.

DETAILED DESCRIPTION

Method and systems relate to generating steam by transitioning waterfrom supercritical conditions and injecting the steam that results intoa formation to facilitate recovery of oil. Pressurizing and heating thewater forms a supercritical fluid that may solvate impurities in thewater and/or oxidize the impurities. Retaining the impurities insolution and/or oxidation of the impurities limits fouling problemsassociated with generating the steam from water recycled in thermalprocesses, such as steam assisted gravity drainage (SAGD), forrecovering the oil.

Turning now to the detailed description of the preferred arrangement orarrangements of the present invention, it should be understood that theinventive features and concepts may be manifested in other arrangementsand that the scope of the invention is not limited to the embodimentsdescribed or illustrated. The scope of the invention is intended only tobe limited by the scope of the claims that follow.

FIG. 1 illustrates an exemplary system that includes an injection well101, a production well 102, a pump 104, a furnace 106, and a letdowndevice for converting a supercritical fluid exiting the furnace 106 intosteam and including at least one of a pressure reducer 108 and a cooler110. While illustrated in an exemplary SAGD configuration, othertechniques, such as cyclic steam stimulation, solvent assisted SAGD,steam drive or huff and puff, may employ the steam generated asdescribed herein. The injection well 101 extends in a horizontaldirection and above the production well 102 also extending in thehorizontal direction.

In operation, the steam enters the formation along the injection well101 forming a steam chamber with heat transferred from the steam to theoil or bitumen in the formation. The oil once heated becomes lessviscous and mobile enough for flowing by gravity along with condensateof the steam to the production well 102. A mixture of the condensate andoil collected in the production well 102 flows to surface where the oilto be sold is separated from the condensate, which is treated andrecycled for generating additional steam to sustain steam injection.

With respect to generating the steam, the pump 104 increases pressure ofwater, including the condensate recycled, to above 22 megapascal (MPa).The furnace 106 then increases temperature of the water to above 375° C.This temperature and pressure at which the water is heated and pumpedforms a supercritical fluid as a result of being above a critical pointof the water.

In some embodiments, impurities or fouling precursors in the water reactwithin the supercritical fluid to form products that do not form solidsupon generation of the steam. These impurities may include dissolvedorganic compounds that react with available oxygen from the water undersupercritical conditions. Products of this reaction include carbondioxide.

The carbon dioxide may pass with the steam into the formation throughthe injection well 101 and may facilitate production of the oil due tosuch influences as dissolution into the oil or thermal insulating.Further, removal of the dissolved organic compounds by this conversionto the carbon dioxide treats the water avoiding buildup of thesecompounds in the water as the water is recycled. According to someembodiments, these reactions result in at least a 50 percent reductionin total organic carbon content by mass in the water.

For some embodiments, the impurities remain solvated by thesupercritical fluid without fouling tube walls of the furnace 106. Thepressure ensures that transition from a liquid phase is to thesupercritical fluid rather than a gas phase that is distinct and maypermit solids to come out of solution. Such solids can cause the foulingif not kept in solution by the supercritical fluid.

The supercritical fluid then flows from the furnace 106 to the pressurereducer 108, such as any flow controller including an orifice plate or avalve. In some embodiments, the pressure reducer 108 drops the pressureto between 3 and 10 MPa or between 9 and 10 MPa, depending on desiredpressures for injection of the steam into the formation. Such pressurereduction may also occur proximate a well pad (e.g., within 1 kilometer(km) of the injection well 101) to limit distance for conveying thesteam or at a central processing facility that may be located 5 to 10 kmor more away from the injection well.

In some embodiments, transitioning the supercritical fluid to the steamrelies on the pressure reducer 108 without further temperatureadjustment other than any line losses. For example, the pressure reducer108 may drop the pressure to provide the steam that is superheated. Useof the steam that is superheated avoids condensation and hence steamloss in transfer lines to the injection well 101 and may also facilitatevaporization of solvents as may be desired for injection with the steam.

For some embodiments, the cooler 110 further contributes to alteringconditions of the supercritical fluid in order to generate the steam. Insome embodiments, the supercritical fluid passes through the cooler 110before the pressure reducer 108. The cooler 110 may inject water intothe steam that is superheated in order to lower the temperature of thesteam to a saturation temperature of the steam or may integrate withother heating needs, such as being used as a heat exchanger to preheatthe water supplied to the furnace 106 while reducing temperature of thesupercritical fluid.

The supercritical fluid may transition to the steam that is wet (e.g.,between 80 and 100 percent quality steam) based on conditions caused bythe cooler 110 and/or the pressure reducer 108 being below a saturatedstate of the steam. At least some of the impurities may remain in aliquid phase when the steam is wet to facilitate removal of theimpurities. For example, a vapor-liquid separator may divide the steamfor injection from liquids for further treatment or disposal.

The following examples of certain embodiments of the invention aregiven. Each example is provided by way of explanation of the invention,one of many embodiments of the invention, and the following examplesshould not be read to limit, or define, the scope of the invention.

EXAMPLE 1

A sample of produced water from an oil sands formation contained aninitial total organic carbon (TOC) content by mass of 3,250 parts permillion (ppm) and total inorganic carbon (TIC) content by mass of 66ppm. The produced water was heated and pressurized to supercriticalconditions. Then, the water was brought back to ambient conditions withresulting steam in such process being condensed and collected to formtreated water.

The treated water contained only 1,140 ppm of TOC and 825 ppm of TICrepresenting a reduction in TOC from the produced water. The TICincreased in the treated water and included bicarbonates dissolved inthe treated water due to oxidation of the organics. This example thusillustrates effectiveness of removing dissolved organics from water tolimit fouling issues in steam generation processes.

In closing, it should be noted that the discussion of any reference isnot an admission that it is prior art to the present invention,especially any reference that may have a publication date after thepriority date of this application. At the same time, each and everyclaim below is hereby incorporated into this detailed description orspecification as additional embodiments of the present invention.

Although the systems and processes described herein have been describedin detail, it should be understood that various changes, substitutions,and alterations can be made without departing from the spirit and scopeof the invention as defined by the following claims. Those skilled inthe art may be able to study the preferred embodiments and identifyother ways to practice the invention that are not exactly as describedherein. It is the intent of the inventors that variations andequivalents of the invention are within the scope of the claims whilethe description, abstract and drawings are not to be used to limit thescope of the invention. The invention is specifically intended to be asbroad as the claims below and their equivalents.

1. A method of generating steam for oil production, comprising:pressurizing and heating water to form a supercritical fluid; convertingat least some of the supercritical fluid to the steam; and injecting thesteam into a formation to facilitate the oil production.
 2. The methodaccording to claim 1, wherein impurities in the water react within thesupercritical fluid to form products that do not form solids upongeneration of the steam.
 3. The method according to claim 1, whereindissolved organic compounds in the water react within the supercriticalfluid to form carbon dioxide that is injected with the steam.
 4. Themethod according to claim 1, wherein dissolved organic compounds in thewater react within the supercritical fluid resulting in at least a 50percent reduction in total organic carbon content by mass in the water.5. The method according to claim 1, wherein the supercritical fluid isconverted to steam that is superheated.
 6. The method according to claim1, wherein impurities in the water remain solvated within thesupercritical fluid during the heating.
 7. The method according to claim1, wherein the supercritical fluid is converted to the steam atconditions below a saturated state to generate the steam that is wet. 8.The method according to claim 1, wherein impurities in the water remainsolvated within the supercritical fluid during the heating and thesupercritical fluid is then converted to the steam at conditions below asaturated state to generate the steam that is wet with the impuritiesremaining in a liquid phase.
 9. The method according to claim 1, whereinthe converting at least some of the supercritical fluid to steamincludes reducing pressure of the supercritical fluid to between 9 and10 megapascals.
 10. The method according to claim 1, wherein theconverting at least some of the supercritical fluid to steam includesreducing pressure of the supercritical fluid from above 22 megapascalsto between 3 and 10 megapascals.
 11. The method according to claim 1,wherein the injecting of the steam is into a horizontal well disposed influid communication with a horizontal producer well for steam assistedgravity drainage production.
 12. The method according to claim 1,wherein the water is pumped to a pressure above 22 megapascals toprovide pressurized water that is then heated to above 375° C. toprovide the supercritical fluid.
 13. A steam generating system for oilproduction, comprising: a pump having a pressurized fluid outlet throughwhich the pump is configured to provide water at above 22 megapascal; afurnace coupled to receive the water from the pressurized outlet of thepump and having a heated fluid outlet through which a supercriticalfluid is provided by the furnace configured to increase temperature ofthe water to above 375° C.; a letdown device coupled to the heated fluidoutlet of the furnace to receive the supercritical fluid and configuredto produce steam from pressure reduction of the supercritical fluid; andan injection well coupled with an outlet of the letdown device forconveying the steam into a formation to facilitate the oil production.14. The system according to claim 13, wherein the letdown device furtherincludes a heat exchanger for cooling the supercritical fluid.
 15. Thesystem according to claim 13, wherein the letdown device includes a flowrestrictor for the pressure reduction of the supercritical fluid. 16.The system according to claim 13, wherein the injection well ishorizontal and disposed in fluid communication with a horizontalproducer well for steam assisted gravity drainage production.
 17. Thesystem according to claim 13, wherein the letdown device is configuredto produce the steam that is superheated.
 18. A method of generatingsteam for oil production, comprising: reducing level of foulingprecursors in water by oxidation of the fouling precursors in the waterat a pressure and temperature above a critical point thereof;transitioning the water from supercritical conditions above the criticalpoint to below the critical point for generation of the steam; andinjecting the steam into a formation to facilitate the oil production.19. The method according to claim 18, wherein the fouling precursorsinclude dissolved organics converted to carbon dioxide for injectingwith the steam.
 20. The method according to claim 18, wherein thereducing the level of fouling precursors includes at least a 50 percentreduction in total organic carbon content by mass in the water.